U.S. patent application number 12/143743 was filed with the patent office on 2009-06-25 for reconstituted wafer level stacking.
This patent application is currently assigned to Tessera, Inc.. Invention is credited to Belgacem Haba, Laura Wills Mirkarimi, llyas Mohammed, Vage Oganesian, David Ovrutsky.
Application Number | 20090160065 12/143743 |
Document ID | / |
Family ID | 40787636 |
Filed Date | 2009-06-25 |
United States Patent
Application |
20090160065 |
Kind Code |
A1 |
Haba; Belgacem ; et
al. |
June 25, 2009 |
Reconstituted Wafer Level Stacking
Abstract
A stacked microelectronic assembly is fabricated from a
structure which includes a plurality of first microelectronic
elements having front faces bonded to a carrier. Each first
microelectronic element may have a first edge and a plurality of
first traces extending along the front face towards the first edge.
After exposing at least a portion of the first traces, a dielectric
layer is formed over the plurality of first microelectronic
elements. After thinning the dielectric layer, a plurality of
second microelectronic elements are aligned and joined with the
structure such that front faces of the second microelectronic
elements are facing the rear faces of the plurality of first
microelectronic elements. Processing is repeated to form the
desirable number of layers of microelectronic elements. In one
embodiment, the stacked layers of microelectronic elements may be
notched at dicing lines to expose edges of traces, which may then
be electrically connected to leads formed in the notches.
Individual stacked microelectronic units may be separated from the
stacked microelectronic assembly by any suitable dicing, sawing or
breaking technique.
Inventors: |
Haba; Belgacem; (Saratoga,
CA) ; Mohammed; llyas; (Santa Clara, CA) ;
Oganesian; Vage; (Palo Alto, CA) ; Ovrutsky;
David; (Charlotte, NC) ; Mirkarimi; Laura Wills;
(Sunol, CA) |
Correspondence
Address: |
TESSERA, INC.
3025 ORCHARD PARKWAY
SAN JOSE
CA
95134
US
|
Assignee: |
Tessera, Inc.
San Jose
CA
|
Family ID: |
40787636 |
Appl. No.: |
12/143743 |
Filed: |
June 20, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11787209 |
Apr 13, 2007 |
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12143743 |
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11704713 |
Feb 9, 2007 |
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11787209 |
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60936617 |
Jun 20, 2007 |
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60850850 |
Oct 10, 2006 |
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Current U.S.
Class: |
257/777 ;
257/E21.001; 257/E23.141; 438/109 |
Current CPC
Class: |
H01L 21/78 20130101;
H01L 2924/01006 20130101; H01L 25/50 20130101; H01L 24/97 20130101;
H01L 2924/15311 20130101; H01L 2924/01005 20130101; H01L 21/6835
20130101; H01L 2225/06506 20130101; H01L 2221/68377 20130101; H01L
2225/06568 20130101; H01L 24/48 20130101; H01L 2224/24145 20130101;
H01L 24/24 20130101; H01L 2224/48227 20130101; H01L 23/5382
20130101; H01L 2924/01033 20130101; H01L 2924/014 20130101; H01L
2924/01082 20130101; H01L 2224/48145 20130101; H01L 2225/06551
20130101; H01L 2225/06517 20130101; H01L 2224/9202 20130101; H01L
2225/06582 20130101; H01L 2924/01078 20130101; H01L 2225/06524
20130101; H01L 2225/0651 20130101; H01L 2224/16225 20130101; H01L
2225/06541 20130101; H01L 24/96 20130101; H01L 2224/48091 20130101;
H01L 2224/97 20130101; H01L 2924/12042 20130101; H01L 2224/16227
20130101; H01L 25/0657 20130101; H01L 2924/00014 20130101; H01L
24/82 20130101; H01L 2224/48091 20130101; H01L 2924/00014 20130101;
H01L 2224/48091 20130101; H01L 2924/00014 20130101; H01L 2224/97
20130101; H01L 2224/82 20130101; H01L 2224/97 20130101; H01L
2924/15311 20130101; H01L 2924/12042 20130101; H01L 2924/00
20130101; H01L 2924/00014 20130101; H01L 2224/45099 20130101; H01L
2924/00014 20130101; H01L 2224/45015 20130101; H01L 2924/207
20130101; H01L 2224/48145 20130101; H01L 2924/00012 20130101 |
Class at
Publication: |
257/777 ;
438/109; 257/E23.141; 257/E21.001 |
International
Class: |
H01L 23/52 20060101
H01L023/52; H01L 21/00 20060101 H01L021/00 |
Claims
1. A method of fabricating a stacked microelectronic assembly
comprising: a) forming a structure comprising a plurality of first
microelectronic elements having front faces bonded to a carrier,
each first microelectronic element having a first edge and a
plurality of first traces extending along said front face towards
said first edge; b) removing material from said first edges to
expose at least a portion of each of said first traces; c) aligning
and joining a plurality of second microelectronic elements with
said structure such that a front face of each said second
microelectronic element is facing a rear face of a first
microelectronic element, each second microelectronic element having
a second edge and a plurality of second traces extending along said
front face of said second microelectronic element towards said
second edge; d) removing material from said second edges to expose
at least a portion of each of said second traces; and e) connecting
leads to said first and second traces.
2. The method of claim 1 wherein said plurality of first
microelectronic elements are spaced apart from one another on said
carrier; and wherein said method further comprises, after step b),
forming a dielectric region between said spaced-apart first
microelectronic elements of said structure.
3. The method of claim 2 further comprising forming openings in
said dielectric region to expose said first and second traces and
forming conductive vias in said openings in conductive
communication with said first and second traces.
4. The method of claim 1 further comprising thinning said structure
comprising said plurality of first microelectronic elements from
said rear faces thereof.
5. The method of claim 1 wherein said step e) further includes
forming notches from a top surface of said stacked microelectronic
assembly to a depth in said stacked microelectronic assembly
sufficient to expose edges of said exposed portions of first and
second traces in walls of said notches; and wherein connecting
leads to said first and second traces comprises forming leads in
said walls of said notches that electrically contact said exposed
edges of said first and second traces.
6. The method of claim 5 wherein forming leads in said walls of
said notches further comprises extending said leads from said walls
to said top surface of said stacked microelectronic assembly.
7. The method of claim 5 further comprising severing said stacked
microelectronic assembly into individual stacked microelectronic
units each comprising at least one of each of aligned first and
second microelectronic elements; wherein at least one wall of one
of said notches with said leads formed thereon forms a side surface
of each individual stacked microelectronic unit.
8. The method of claim 1 further comprising severing said plurality
of joined first and second microelectronic elements into individual
units each including first and second aligned microelectronic
elements and leads extending from said first and second traces.
9. The method of claim 1 wherein said step (a) further comprises
selecting individual ones of said first microelectronic elements
from a plurality of unattached first microelectronic elements for
bonding to said carrier.
10. The method of claim 1 wherein step c) of aligning and joining
said plurality of second microelectronic elements with said
structure comprises positioning each of said second microelectronic
elements such that said second edge of each second microelectronic
element is substantially aligned with said first edge of each said
first microelectronic element.
11. The method of claim 1 wherein step c) of aligning and joining
said plurality of second microelectronic elements with said
structure comprises positioning each of said second microelectronic
elements such that said second edge of each second microelectronic
element is laterally offset from said first edge of each said first
microelectronic element.
12. The method of claim 1 wherein each of said first and second
microelectronic elements comprises a flash memory.
13. A method of fabricating a stacked microelectronic assembly
comprising: a) forming a first structure comprising a plurality of
spaced-apart first microelectronic elements each having a front
face bonded to a carrier layer and an opposing rear face; each
first microelectronic element comprising a plurality of first
traces extending along said front face towards a first edge of said
microelectronic element; b) from said rear face, removing material
from said first edge of each first microelectronic element until at
least a portion of each of said first traces is exposed; c) forming
a dielectric layer over said plurality of spaced-apart first
microelectronic elements; said dielectric layer forming a
dielectric region between said spaced-apart first microelectronic
elements; d) from said rear faces, thinning said dielectric layer
and said plurality of spaced-apart first microelectronic elements
to a desired thickness; e) forming a second structure comprising a
plurality of spaced-apart second microelectronic elements by (i)
aligning said plurality of spaced-apart second microelectronic
elements with said plurality of spaced-apart first microelectronic
elements such that a front face of each said second microelectronic
element is facing a rear face of a first microelectronic element,
and (ii) by joining said plurality of spaced-apart and aligned
second microelectronic elements to said first structure; each
second microelectronic element having a second edge and a plurality
of second traces extending along said front face of said second
microelectronic element towards said second edge; f) from said rear
face, removing material from said second edge of each second
microelectronic element until at least a portion of each of said
second traces is exposed; g) forming a dielectric layer over said
plurality of spaced-apart second microelectronic elements; said
dielectric layer forming a dielectric region between said
spaced-apart second microelectronic elements; h) from said rear
faces, thinning said dielectric layer and said plurality of
spaced-apart second microelectronic elements to a desired
thickness; i) forming notches from a top surface of said second
structure to a depth in said stacked microelectronic assembly
sufficient to expose a cross-sectional edge of each portion of said
first and second traces in walls of said notches; and j) forming
leads in said walls of said notches; said leads electrically
connecting said exposed edges of said first and second traces; said
leads extending from said walls to said top surface of said stacked
microelectronic assembly.
14. The method of claim 13 wherein said step e) (i) of aligning
said plurality of spaced-apart second microelectronic elements with
said plurality of spaced-apart first microelectronic elements
further comprises aligning said second edge of each said second
microelectronic element with said first edge of each said first
microelectronic element.
15. The method of claim 13 wherein said step e) (i) of aligning
said plurality of spaced-apart second microelectronic elements with
said plurality of spaced-apart first microelectronic elements
further comprises positioning each second microelectronic element
such that said second edge of each second microelectronic element
is laterally offset from said first edge of each said first
microelectronic element.
16. The method of claim 13 wherein each of said first and second
microelectronic elements comprises a flash memory.
17. A microelectronic device having at least two side external
surfaces; said microelectronic device comprising: a first
substrate; a first microelectronic element comprising a front face
bonded to said first substrate and an opposing rear face; said
first microelectronic element further comprising a plurality of
first traces extending along said front face; at least a portion of
each said first trace extending beyond a first edge of said first
microelectronic element; said first microelectronic element further
comprising a second edge opposite said first edge; a first
insulating region disposed around said first and second edges of
said first microelectronic element; a second microelectronic
element comprising a front face facing said opposing rear face of
said first microelectronic element; said second microelectronic
element further comprising a plurality of second traces extending
along said front face; at least a portion of each said second trace
extending beyond a first edge of said second microelectronic
element; said second microelectronic element further comprising a
second edge opposite said first edge; a second insulating region
disposed around said first and second edges of said second
microelectronic element; and at least one electrical conductor
disposed on at least one of said side external surfaces of said
microelectronic device; said electrical conductor being in electric
contact with a cross-sectional edge of at least one of said
plurality of said first and second traces.
18. The microelectronic device of claim 17 wherein said first and
second edges of second microelectronic element are substantially
aligned with said first and second edges of said first
microelectronic element.
19. The microelectronic device of claim 17 wherein said first edge
of said second microelectronic element is laterally offset from
said first edge of said first microelectronic element.
20. The microelectronic device of claim 17 wherein each of said
first and second microelectronic elements comprises a flash memory.
Description
BACKGROUND
[0001] The subject matter of the present application relates to
microelectronic packages, or assemblies, comprised of stacked
microelectronic elements and to methods of fabricating them, for
example, by processing applied simultaneously to a plurality of
microelectronic elements arranged in an array.
[0002] Microelectronic elements, such as semiconductor chips, are
flat bodies with contacts disposed on the front surface that are
connected to the internal electrical circuitry of the element
itself. Microelectronic elements are typically packaged with
substrates to form microelectronic packages, or assemblies, having
terminals that are electrically connected to the element's
contacts. The package or assembly may then be connected to test
equipment to determine whether the packaged device conforms to a
desired performance standard. Once tested, the package may be
connected to a larger circuit, e.g., a circuit in an electronic
product such as a computer or a cell phone.
[0003] Microelectronic packages or assemblies also include wafer
level packages, which provide a package for a microelectronic
component that is fabricated while the die are still in a wafer
form. The wafer is subject to a number of additional process steps
to form the package structure and the wafer is then diced to free
the individual die. Wafer level processing may provide a cost
savings advantage. Furthermore, the package footprint can be
identical to the die size, resulting in very efficient utilization
of area on a printed circuit board (PCB) to which the die will
eventually be attached. As a result of these features, die packaged
in this manner are commonly referred to as wafer-level chip scale
packages (WLCSP).
[0004] In order to save space certain conventional designs have
stacked multiple microelectronic chips or elements within a package
or assembly. This allows the package to occupy a surface area on a
substrate that is less than the total surface area of all the chips
in the stack added together. Development efforts in this technology
focus on producing wafer-level assemblies that are reliable, or
thin, or testable, or which are economical to manufacture, or have
a combination of such characteristics.
SUMMARY
[0005] A method is provided for fabricating a stacked
microelectronic assembly from a structure which includes a
plurality of first microelectronic elements having front faces
bonded to a carrier. Each first microelectronic element may have a
plurality of first edges and a plurality of first traces extending
along the front face towards the first edges. After exposing the
first traces, a dielectric layer is formed over the plurality of
first microelectronic elements. After thinning the dielectric
layer, a plurality of second microelectronic elements are aligned
and joined with the structure such that front faces of the second
microelectronic elements are adjacent to rear faces of the
plurality of first microelectronic elements. Processing is repeated
to form the desirable number of layers of microelectronic elements.
In one embodiment, the stacked layers of microelectronic elements
may be notched at dicing lines to expose edges of traces, which may
then be electrically connected to leads formed in the notches.
Individual stacked microelectronic units may be separated from the
stacked microelectronic assembly by any suitable dicing, sawing or
breaking technique.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The structure and methods of fabrication of the
microelectronic devices described herein are best understood when
the following description of several illustrated embodiments is
read in connection with the accompanying drawings wherein the same
reference numbers are used throughout the drawings to refer to the
same or like parts. The drawings are not necessarily to scale;
emphasis has instead been placed upon illustrating the structural
and fabrication principles of the described embodiments. The
drawings include:
[0007] FIG. 1A is a top plan view of a wafer, or portion of a
wafer, comprising microelectronic elements;
[0008] FIG. 1B is an enlarged portion of one of the microelectronic
elements disposed on the wafer of FIG. 1A;
[0009] FIG. 1C is a side elevation view of a portion of the wafer
of FIG. 1A taken at line 1B of FIG. 1A;
[0010] FIG. 2 is a side elevation view of several individual
microelectronic elements separated from the wafer of FIG. 1A;
[0011] FIG. 3 is an elevated side view of a reconstituted wafer
structure comprising individual microelectronic elements selected
from the microelectronic elements of FIG. 2;
[0012] FIG. 4 is a cross-sectional view of the reconstituted wafer
structure of FIG. 3 after an etchant is supplied to channels
running between individual ones of the microelectronic elements to
remove material from the edges of the microelectronic elements;
[0013] FIG. 5 is a cross-sectional view of the reconstituted wafer
structure of FIG. 4 after a dielectric layer is formed over the
structure;
[0014] FIG. 6 is a cross-sectional view of the reconstituted wafer
structure of FIG. 5 after the dielectric layer and microelectronic
elements have been thinned to a desired height;
[0015] FIGS. 7A, 7B and 7C are cross-sectional views of a second
reconstituted wafer structure being formed over the reconstituted
wafer structure of FIG. 6;
[0016] FIG. 7D is a cross-sectional view of a stacked
microelectronic assembly comprising four reconstituted wafers;
[0017] FIG. 8 is a sectional view illustrating a stage of
fabrication of stacked microelectronic assembly subsequent to that
shown in FIG. 7D in which notches are cut into the assembly;
[0018] FIG. 9 is a sectional view of stacked microelectronic
assembly after notches have been created, showing the formation of
leads on the side walls of the notches;
[0019] FIGS. 10A, 10B and 10C illustrate various embodiments of
individual stacked microelectronic units produced from the
embodiment of stacked microelectronic assembly of FIG. 9;
[0020] FIG. 11 is an exemplary embodiment of the individual stacked
microelectronic unit of FIG. 10A electrically connected to an
interconnection element;
[0021] FIG. 12 is a partial top plan view 200 of the stacked
microelectronic assembly of FIG. 7D and showing openings made
between adjacent microelectronic elements;
[0022] FIG. 13 shows a series of side elevation views of structures
illustrating initial stages in the formation of stacked
microelectronic units according to a second embodiment;
[0023] FIG. 14 shows a series of side elevation views of structures
illustrating the next stages in the formation of stacked
microelectronic units according to the second embodiment;
[0024] FIG. 15 is a sectional view of the stacked microelectronic
assembly produced by the processes illustrated in FIGS. 13 and
14;
[0025] FIG. 16 is a sectional view of the stacked microelectronic
assembly of the second embodiment, after notches have been formed
between adjacent microelectronic elements;
[0026] FIG. 17 is a top plan view of a portion of the stacked
microelectronic assembly of FIG. 16 illustrating the redistribution
of electrical signals from a set of contacts at a first edge of a
microelectronic element to a second edge; and
[0027] FIGS. 18 and 19 pictorially illustrate manufacturing
apparatus and processes used in the fabrication of the stacked
microelectronic units described and shown herein.
DETAILED DESCRIPTION
First Embodiment of Method of Fabrication of Stacked
Microelectronic Assembly
[0028] FIGS. 1A-1C illustrate an array, or a portion of an array,
of microelectronic elements. FIG. 1A is a top plan view of wafer
10, or portion of a wafer 10, and includes a plurality of
microelectronic elements shown as rectangles. Wafer 10 preferably
includes numerous rows of microelectronic elements aligned along an
X-axis and a Y-axis, in the form of an array. Wafer 10 may include
any number of microelectronic elements including as little as two
or as many as is desirable. Wafer 10 in FIG. 1A has a top edge 15,
a right edge 13, a left edge 11 and a bottom edge 17. FIG. 1C is an
elevated side view of wafer 10 taken along line 1B (FIG. 1A),
showing left edge 11 and right edge 13 of wafer 10. FIG. 1C also
shows that each microelectronic element of wafer 10 also has a
front face 14 and an oppositely-facing rear face 16. Note that in
FIG. 1C, the front face 14 of wafer 10 has been turned over to face
down in the figure.
[0029] In FIG. 1A, three microelectronic elements 12, 12'' (twelve
double prime) and 12' (twelve prime) are individually called out in
the middle row of wafer 10. The wafer can be in the shape of a
circular wafer. Hereinafter, for ease of reference, the wafer 10 or
wafer portion is referred to as a "wafer". The microelectronic
elements are formed integral with one another using semiconductor
fabrication techniques. Each of the microelectronic elements of the
wafer is typically of the same type. The microelectronic elements
can have memory function, logic or processor function or a
combination of logic and processor functions, among other possible
types. In a particular example, each of the microelectronic
elements includes a flash memory. For example, each microelectronic
element can be a dedicated flash memory chip.
[0030] With reference to microelectronic element 12 of FIG. 1A,
each microelectronic element has a first edge 18, a second edge 20,
a third edge 19 and a fourth edge 21. When microelectronic element
12 is still part of the array of wafer 10, a first edge 18 of one
microelectronic element 12 abuts (or is attached to) second edge 20
of a second and adjacent microelectronic element 12. Similarly, a
third edge 19 (FIG. 1A) of one microelectronic element 12 is
attached to a fourth edge 21 of an adjacent microelectronic
element. Thus, a microelectronic element 12'' positioned in a
middle row of the wafer portion 10 is bordered by an adjacent
microelectronic element at all four edges, as shown in FIG. 1A.
When microelectronic element 12 is entirely separated from wafer 10
(e.g., singulated thereform), it can be seen that each of first
edge 18, second edge 20, third edge 19 and fourth edge 21 extends
from the front face 14 (FIG. 1C) to the rear face 16 (FIG. 1C) of
the microelectronic element 12.
[0031] Portions of wafer 10 where adjacent microelectronic elements
contact one another form saw lanes or strips 23 and 25 where the
wafer can be cut without damaging the individual microelectronic
elements. For instance, as shown in FIG. 1C, second edge 20' of
microelectronic element 12' abuts first edge 18'' of
microelectronic element 12'' and forms a saw lane 23. Similarly,
throughout the wafer 10, saw lanes 23 (shown in FIGS. 1A and 1C)
are located at positions where the microelectronic elements abut
one another.
[0032] With reference to microelectronic element 12'' of FIG. 1B,
each microelectronic element includes a plurality of contacts 22''
exposed at the respective front face 14 of the microelectronic
element 12. The contacts 22 can be, for example, bond pads or lands
of the microelectronic elements as originally formed in a wafer
fabrication facility. Each microelectronic element of the uncut
wafer 10 has a device region 26 (area bounded by dashed lines 27)
in which active semiconductor devices and typically also passive
devices are disposed. Each microelectronic element also includes a
non-device region disposed beyond edges of the device region 26
where no active semiconductor devices or passive devices are
disposed. Note that the bounded area of device region 26 is shown
by solid lines in FIG. 1C. A trace 24 extends outwardly from each
of the contacts 22 to a respective first, second, third or fourth
edge 18, 20, 19, and 21 of each individual microelectronic element,
crossing between the device region 26 and non-device region. For
example, with reference to FIG. 1B, trace 24' extends outwardly
from contact 22' towards the second edge 20' of microelectronic
element 12' (FIG. 1A). The trace 24' extends to and contacts trace
24'', which extends outwardly from contact 22''. Thus, traces 24'
and 24'' meet at the attachment point of microelectronic elements
12' and 12'' and may actually form a single trace extending between
contact 22' and contact 22''. However, it is not required that the
traces actually contact one another. Similar structures may be
included for all adjacent microelectronic elements 12. The traces
24 may be formed in the wafer fabrication facility at the same time
or after the contacts 22 of the wafer are fabricated.
Alternatively, the traces 24 may be formed by subsequent processing
after the wafer 10 leaves the wafer fabrication facility, such as
at a facility where processing as described below is performed.
[0033] In one stacked assembly fabrication embodiment, an assembly
including a plurality of stacked microelectronic elements is
fabricated by simultaneously processing a plurality of
microelectronic elements en masse. Moreover, processing can be
carried out simultaneously as to microelectronic elements which are
arranged in form of an array, similar to the processing of an
original wafer containing such microelectronic elements. FIGS. 2-7B
illustrate stages in a method of forming a package or assembly of
stacked microelectronic elements in accordance with a first
fabrication embodiment. In this embodiment, original wafer 10 is
first separated into individual microelectronic elements and then
selected ones of the individual microelectronic elements are
arranged in form of an array for further processing. In this
embodiment, the array of selected microelectronic elements can be
considered a "reconstituted wafer" which is then available for
processing according to wafer-level processing techniques. FIG. 2
illustrates a stage of fabrication in which an original wafer 10 is
separated into individual microelectronic elements 12 by severing,
e.g., sawing or scribing wafer 10 along the dicing lanes 23 and 25
(FIG. 1A). FIG. 3 is an elevated side view of reconstituted wafer
structure 90 comprising individual microelectronic elements 112
that were selected from the microelectronic elements 12 obtained
during the dicing (sawing) stage of FIG. 2. Individual
microelectronic elements 112 are referred to as the known good die,
and are attached in a face down position (i.e., with the front face
of the die on which are disposed traces 24 and contacts 22) to a
carrier 160 using an adhesive 162. A pick-and-place tool can be
used to place each microelectronic element 112 at the proper
position on the carrier 160 to form reconstituted wafer structure
90.
[0034] An advantage of processing reconstituted wafers rather than
the original wafer 10 is that the microelectronic elements that
make up each reconstituted wafer can be individually selected. In
this way, when some of the microelectronic elements of the original
wafer are of known or suspected marginal or failing quality, they
need not be processed into stacked assemblies. Rather, those
microelectronic elements can be left out of the reconstituted wafer
such that the reconstituted wafer contains better quality
microelectronic elements. Selection of the microelectronic elements
to go into the reconstituted wafer can be made based on various
criteria of quality or expected quality based on visual inspection,
mechanical or electrical inspection or location of the
microelectronic element within the original wafer 10. In a
particular embodiment, microelectronic elements may in fact be
tested electrically before placing each one into position on the
reconstituted wafer. Whether the microelectronic elements are
selected based on visual inspection, location or electrical test
results, the microelectronic elements which are selected for
inclusion in the reconstituted wafer can be referred to as "known
good" microelectronic elements or "known good die".
[0035] Next, as illustrated in FIG. 4, an etchant is supplied to
channels 114 which run between individual ones of the
microelectronic elements 112 of reconstituted wafer 90. The etchant
is used to remove material from the edges of the microelectronic
elements. As a result of this step, portions of the traces 24 at
the front face of each microelectronic element become exposed
within the channels.
[0036] As illustrated in FIG. 5, a dielectric layer 116 is then
formed over reconstituted wafer structure 90 of FIG. 4. Dielectric
layer 116 fills channels 114 of reconstituted wafer structure 90,
thereby covering rear faces 118 of the microelectronic elements
112. The dielectric layer can include one or more inorganic
dielectric materials such as an oxide, nitride, which may include
silicon dioxide, silicon nitride or other dielectric compound of
silicon such as SiCOH, among others, or may include an organic
dielectric, among which are various polymers such as epoxy,
polyimide, among others. FIG. 6 is a side elevation view of
reconstituted wafer structure 110 which is produced by reducing the
thickness of each microelectronic element and dielectric layer 116
to a desired thickness by lapping, grinding or polishing
reconstituted wafer structure 90 of FIG. 5 from the rear faces 118
of each microelectronic element 112.
[0037] With reference to FIG. 7A, a next layer of known good die
are then processed using reconstituted wafer 110 as a base or
carrier layer. A second layer of known good microelectronic
elements 112A are selected and attached to reconstituted wafer 110
using adhesive layer 162A which is deposited over reconstituted
wafer 110. Desirably, the second layer of microelectronic elements
is attached in registration with corresponding ones of the first
microelectronic elements 112. The second layer of known good
microelectronic elements 112A is processed in a manner similar to
the process shown and described above with reference to FIGS. 4
through 6; that is, an etchant is supplied to channels 114A which
run between individual ones of the microelectronic elements 112A of
the second reconstituted wafer layer in order to remove material
from the edges of microelectronic elements 112A so as to expose
portions of the traces 24 within the channels at the front face of
each microelectronic element. As shown in FIG. 7B, dielectric layer
116A is then formed over the second reconstituted wafer layer of
FIG. 7A to fill channels 114A, thereby covering rear faces 118 of
the microelectronic elements 112A. Then the thickness of each
microelectronic element 112A and dielectric layer 116A is reduced
to a desired thickness by lapping, grinding or polishing the second
reconstituted wafer layer of FIG. 7B from the rear faces 118 of
each microelectronic element 112A. At the conclusion of this
processing, a second reconstituted wafer 110A is formed, as shown
in FIG. 7C.
[0038] Thereafter, with reference to FIG. 7D, if it is desired to
add further layers of microelectronic elements to the stack of
microelectronic elements of FIG. 7C, an adhesive layer is formed to
overlie microelectronic elements 112A and a third layer of
microelectronic elements 112B are then attached to that adhesive
layer and processed in a manner similar to the process shown and
described above with reference to FIGS. 7A through 7C to form third
reconstituted wafer 110B. A fourth layer of microelectronic
elements 112C may also be formed in a similar manner by forming an
adhesive layer over microelectronic elements 112B and attaching a
fourth layer of microelectronic elements 112C to that adhesive
layer and subsequently processing the fourth layer in the same
manner as described above to form fourth reconstituted wafer 110C.
The thickness of carrier layer 160 (FIG. 7C) may be reduced at this
time using any suitable lapping, grinding or polishing process to
form reduced carrier layer 160A. In addition, a protective layer
164 including a dielectric and which may include an adhesive (not
separately shown in the figure) may be formed to cover the
uppermost layer of microelectronic elements 112C. Together this
processing forms stacked assembly 30.
[0039] FIG. 8 is a sectional view illustrating a stage of
fabrication of stacked assembly 30 subsequent to that shown in FIG.
7D. The processing illustrated with reference to FIGS. 8-10 need
not be performed in any particular orientation; the individual
microelectronic elements in stacked assembly 30 may have front
faces oriented upwardly, downwardly or to a side. Referring to FIG.
8, a plurality of notches 46 are cut into the stacked assembly 30.
The notches 46 are preferably formed using a mechanical cutting
instrument not shown in the figures. Examples of such a mechanical
cutting instrument can be found in U.S. Pat. Nos. 6,646,289 and
6,972,480, the disclosures of which are hereby incorporated by
reference herein. Alternatively, a laser drilling technique can be
used to form notches 46. As compared to FIG. 7D and as shown in
FIG. 8, notches 46 are cut from the stacked assembly 30 at
locations between microelectronic elements that are horizontally
adjacent in their respective reconstituted wafers 110, 110A, 110B
and 110C. With reference back to FIGS. 1A, 1B and 1C, these
locations are proximate to respective first edges 18 and second
edges 20 of each microelectronic element. Although not shown in the
sectional view of FIG. 8, notches may also be formed in locations
that are proximate to respective third edges 19 and fourth edges 21
of each microelectronic element in reconstituted wafers 110, 110A,
110B and 110C.
[0040] In the embodiment shown in FIG. 8, the individual
microelectronic elements in each reconstituted wafer 110, 110A,
110B and 110C are aligned throughout stacked assembly 30. Thus, a
single cut may be used to form notches 47 between individual
stacked microelectronic elements. In the embodiment shown in FIG.
8, notches 46 do not extend entirely through stacked assembly 30.
For instance, as shown in FIG. 8, the microelectronic elements of
reconstituted wafer 110 remain attached to each other as the
various notches 46 do not extend entirely through reduced carrier
layer 160A underlying first reconstituted wafer 110. However,
notches 46 are sufficiently wide and deep so as to intersect, and
thus expose the edges of, traces 24 (represented as dark thick
horizontal lines) that extend out from the contacts disposed on the
front faces of the individual microelectronic elements of each
reconstituted wafer 110, 110A, 110B and 110C. In the embodiment of
FIG. 8, notches 46 are illustrated having inclined side walls 48,
50. In another embodiment not illustrated in a figure herein, the
side walls may be straight, i.e., oriented in a normal direction to
a plane defined by the front faces of the microelectronic
elements.
[0041] First exposed side edge 170 and second exposed side edge 172
of stacked assembly 30 need not be cut to expose edges of the
traces because the edges of the traces (represented as dark thick
horizontal lines) that extend toward these respective edges are
already exposed. In another embodiment not illustrated in a figure
herein, first and second side edges 170 and 172 may be cut so as to
create a more symmetrical configuration. Similarly, the other two
side edges of stacked assembly 30 not shown in the figures also do
not have to be cut, although it may be desirable to do so.
[0042] FIG. 9 is a sectional view of stacked assembly 30 after
notches 46 have been created, showing the formation of leads 66 on
the side walls 48, 50 (FIG. 8) of notches 46. Leads 66 may be
formed by any suitable metal deposition technique, for example, a
process that includes sputtering, three-dimensional lithography and
electroplating. Additional processes may also be employed. One such
process is disclosed in U.S. Pat. No. 5,716,759, the disclosure of
which is hereby incorporated by reference herein. Depending on the
particular process used, lead formation may comprise the depositing
a metal layer across the entire length and depth of a notch 46, and
then etching the metal away in areas where there are no exposed
edges of traces 24. When the lead formation process is completed,
each of a set of individual leads 66 extends within a notch 46 at
the location of the exposed edges of a set of aligned traces 24 of
reconstituted wafers 110, 110A, 110B and 110C, thereby establishing
electrical contact with the exposed edges of that set of traces 24.
In the embodiment shown in FIG. 9, leads 66 include end lead
portion 75 which extends past the side wall of each notch 46 onto
protective layer 164 positioned above reconstituted wafer 110C. If
protective layer 164 is not provided, end lead portion 75 extends
past the side wall of each notch 46 onto the rear face of the
individual microelectronic elements that form reconstituted wafer
110C. Pads or solder bumps 74 may be formed to be in contact with
end lead portion 75 as shown.
[0043] With continued reference to FIG. 9, when traces 24 disposed
on the face of individual microelectronic elements in each
reconstituted wafer 110, 110A, 110B and 110C in a stack are in
alignment among the respective reconstituted wafers, each lead 66
is in contact with all of the edges of the traces 24 exposed at a
respective side wall of notch 46. However, in another embodiment, a
lead 66 may be in electrical connection with fewer than all of the
traces 24 of the stacked microelectronic elements in a set of
reconstituted wafers 110, 10A, 110B and 11C when traces 24 disposed
on one microelectronic element in one reconstituted wafer layer are
not in exact alignment or lie in different planes than traces 24
disposed on microelectronic elements in a second, third or fourth
reconstituted wafer layer.
[0044] With continued reference to FIG. 9, after notches 46 and
conductive elements including leads 66, end lead portions 75 and
solder bumps 74 are formed on stacked assembly 30, reduced carrier
layer 160A of stacked assembly 30 may be severed by mechanically
cutting or, alternatively, scribing and breaking reconstituted
wafer 110 at locations 90 proximate to notches 46. In this way, a
plurality of individual units are produced, with each individual
unit containing a plurality of microelectronic elements stacked one
upon another.
[0045] FIGS. 10A and 10B illustrate two embodiments of individual
units 80 and 81 from the embodiment of stacked assembly 30 of FIG.
9 with inclined sidewalls in which the severing, or singulation,
process at locations 90 of FIG. 9 achieves different profiles,
depending on the method used and the precision of the cutting
instrument, if one is used. As noted above, individual units
produced from a stack of microelectronic elements need not have
inclined sidewalls; single units with sidewalls normal to reduced
carrier layer 160A are not illustrated in the figures. Also noted
above, individual units produced from the stacked reconstituted
wafers of microelectronic elements located at the ends of stacked
assembly 30 may or may not have inclined sidewalls all around. FIG.
10C illustrates individual unit 82 produced after singulation from
the embodiment of stacked assembly 30 of FIG. 9 that includes left
edge 170.
[0046] Any one of individual stacked assemblies 80, 81 or 82 of
FIG. 10A, 10B or 10C can be electrically connected to other
electronic elements or substrates. FIG. 11 is an exemplary
embodiment of stacked assembly 80, shown inverted from the view in
FIG. 10A, electrically connected via solder bumps 74 to an
interconnection element 210, e.g., a dielectric element, substrate,
circuit panel or other element having terminals 84, 86 and
conductive wiring therein. One or more additional microelectronic
elements 230 can be attached to the face of assembly 80 opposite
the face comprising solder bumps 74 and electrically interconnected
by bond wires 88 to terminals 84 of the interconnection element
210. Examples of microelectronic element 230 may include one or
more additional microelectronic elements which supplement the
function of the stacked assembly, such as, by way of example and
not intended to be exhaustive, a microcontroller. Microelectronic
element 230 may include one or more redundancy elements for
substitution with one or more of the individual microelectronic
elements in stacked individual unit 80, in case of a problem with
such microelectronic element. In a particular embodiment, the
stacked individual unit 80 may be incorporated into
microprocessors, and RF units among other assemblies. One or more
stacked units 80 may incorporate particular types of
microelectronic elements such as flash memory or dynamic random
access memory (DRAM) units and be incorporated in various units
including memory modules, memory cards, and the like. Other
exemplary arrangements for electrically connecting stacked
individual unit 80 to an interconnection element, and for mounting
additional microelectronic elements to stacked individual unit 80
are shown and described in commonly owned U.S. patent application
Ser. No. 11/787,209 filed Apr. 13, 2007, the disclosure of which is
hereby incorporated herein by reference.
Embodiments of Stacked Microelectronic Assemblies Using Vias to
Provide Electrical Access Conductive Traces
[0047] With reference to FIGS. 7D and 8, electrical access to
conductive traces 24 in all reconstituted wafer layers 110, 110A,
110B and 110C is achieved by cutting notches 46 into stacked
assembly 30 in the manner shown in these figures and described
above with reference thereto, in order to expose the edges of
conductive traces 24 to the later-applied leads 66 (FIG. 9). Lead
formation is achieved by using a suitable metal deposition
technique to deposit a metal layer onto the surfaces of each notch
46. Such metal deposition techniques may require metal etching to
form leads that provide electrical access to only the exposed edges
of traces disposed on the front faces of the microelectronic
elements that are vertically aligned in the reconstituted wafer
layers 110C, 110B, 110A and 110.
[0048] In another embodiment, electrical access may be made to
conductive traces 24 in reconstituted wafer layers 110, 110A, 110B
and 110C by making openings, or vias, into stacked assembly 30 at
the locations of the traces, using any suitable drilling technique,
such as a laser drilling technique. FIG. 12 is a partial top plan
view 200 of stacked assembly 30 of FIG. 7D looking down at top
reconstituted wafer 110C, assuming for purposes of this discussion
that protective layer 164 is at least partially transparent or is
not present in this embodiment. Openings, or vias, 228 are
represented by small grey circles; while not labeled as such, it is
to be understood from the figure that each grey circle represented
is an opening 228. In FIG. 12, representative ones of openings 228
are formed in saw lanes 218 and 220 of reconstituted wafer 110C
between adjacent microelectronic elements and extend through
stacked assembly 30 to reach to reconstituted wafer 110. Each
opening 228 thus exposes the edges of all of the traces 24 disposed
on the front faces of each of the pairs of vertically aligned and
adjacent microelectronic elements in all of reconstituted wafer
layers 110C, 110B, 110A and 110. The individual openings 228 are
plated using a suitable metal deposition technique, after which a
singulation (e.g., dicing) process produces individual stacked
microelectronic units from stacked assembly 30 similar to those
shown in FIGS. 10A, 10B and 10C.
[0049] In another embodiment, using the technique described above
with respect to FIG. 12, electrical access may be made to all or
selective ones of the conductive traces 24 in selective ones of
reconstituted wafer layers 110, 110A, 110B and 110C by making
openings to selected depths into stacked assembly 30 at selected
locations.
Stacked Microelectronic Unit Embodiment Comprising Offset
Microelectronic Elements
[0050] FIGS. 13-17 illustrate another embodiment for forming
stacked microelectronic units. FIG. 13 shows a series of side
elevation views of structures illustrating initial stages in the
formation of stacked microelectronic units according to this
embodiment. Microelectronic elements 32 having bond pads 22
connected to traces 24 are separated from an original wafer (not
shown) along saw lines 23. Selected microelectronic elements 312
(e.g., known good die) from among microelectronic elements 32 are
attached to carrier 160 using adhesive layer 162 to form
reconstituted wafer structure 390. Then, in a manner similar to the
processes described with respect to FIGS. 4 and 5 above, an etchant
is supplied to channels 114 which run between individual ones of
the microelectronic elements 312 to remove material from the edges
of the microelectronic elements in order to expose within channels
114 portions of the traces 24 at the front face of each
microelectronic element 312. A dielectric layer 116 is then formed
over reconstituted wafer structure 390 to fill channels 114,
thereby covering rear faces 118 of the microelectronic elements 312
and producing reconstituted wafer structure 392.
[0051] FIG. 14 shows a series of side elevation views of structures
illustrating the next stages in the formation of stacked
microelectronic units according to this embodiment. Reconstituted
wafer structure 392 of FIG. 13 is then thinned to produce
reconstituted wafer 310 by reducing the thickness of each
microelectronic element and dielectric layer 116 to a desired
thickness by lapping, grinding or polishing reconstituted wafer
structure 392 from the rear faces 118 of each microelectronic
element 312. Arrows 350 mark the lateral position of each edge 340
of each microelectronic element of reconstituted wafer 310.
[0052] After thinning first reconstituted wafer 310 to the desired
thickness, the microelectronic elements 312A needed to form a
second reconstituted wafer 310A are bonded to reconstituted wafer
310 such that an edge 340A of a microelectronic element 312A of the
second reconstituted wafer structure to be formed occurs at
position 350A which is offset in a lateral direction 360 from the
edge 340 of the first reconstituted wafer 310. Thus, when referring
to microelectronic elements 312A of the second reconstituted wafer
as the overlying microelectronic elements and microelectronic
elements 312 of the first reconstituted wafer 310 as the underlying
microelectronic elements, overlying microelectronic elements 312A
each has an area overlapping an area of the underlying
microelectronic element 312 to which it is bonded, and each has an
edge 340A that is displaced in the lateral direction 360 from the
edge 340 of the underlying microelectronic element 312. An
exemplary distance of the lateral offset between edges of
vertically adjacent overlapping microelectronic elements can range
from a few microns to tens of microns or more.
[0053] With continued reference to FIG. 14, the formation of second
reconstituted wafer 310A is completed with the etching process, the
application of the dielectric layer, and thinning process shown in
FIG. 13 with respect to reconstituted wafer 310, omitted in FIG.
14. The sub-processes shown in FIG. 14 are repeated for forming a
third reconstituted wafer 310B containing microelectronic element
312B and a fourth reconstituted wafer 310C containing
microelectronic element 312C to form the stacked assembly 330 shown
in FIG. 15. As illustrated in FIG. 16, notches 346 are then cut
between adjacent elements to expose the edges of the traces
disposed on the front faces of the microelectronic elements in each
reconstituted wafer 310, 310A, 310B and 310C.
[0054] An advantage of forming the stacked assembly in this manner
is that process tolerances can improve for forming leads 366 (FIG.
16) adjacent to the exposed edges of the traces at the sidewalls of
notch 46. The lateral displacement of each succeeding overlapping
microelectronic element in the stacked assembly allows for slope in
the sidewalls of each notch 346 formed therein. Increased lateral
displacement allows the sidewalls of each notch 346 to be more
heavily sloped, i.e., at a greater angle from the vertical.
"Vertical" is defined herein as a normal angle to the plane defined
by the contact-bearing surface of a microelectronic element, e.g.,
element 312. Despite greater slope of the wall, the notching
operation, performed, e.g., by cutting or laser drilling exposes
trace edges even when the length of such traces is limited.
Particularly when the traces 324 are formed on each original wafer
(FIGS. 1A-B) prior to dicing and forming reconstituted wafers,
traces 324 can have very limited length.
[0055] With reference to FIG. 17, when the microelectronic elements
312 are provided with contact pads adjacent to edges 340 and 342, a
redistribution layer including additional traces 326 can be
provided which extends between the pads at edge 342 and outwardly
beyond a third edge 344 of the microelectronic element 312. When
forming the stacked assembly, 330, overlapping microelectronic
elements of each successively stacked reconstituted wafer 310,
310A, 310B and 310C can be offset as well in a direction 362. In
this way, leads can be formed in notches which expose traces 326
along the third edges 344 of the overlapping microelectronic
elements, and process tolerance can also be improved for forming
such leads.
Fabrication Embodiment of Stacked Microelectronic Assembly
[0056] Reference is now made to FIGS. 18 and 19, which are
illustrations of apparatus employed in the manufacture of
assemblies of the types discussed herein. As seen in FIGS. 18 and
19, a conventional wafer fabrication facility 680 provides complete
wafers 681, of the type partially shown in FIGS. 1A and 1B.
Individual microelectronic elements or chips 682 are bonded on
their active surfaces to a carrier layer or protective layer 683 by
bonding apparatus 685, such as by way of a layer of adhesive, e.g.,
epoxy (not shown). The apparatus 685 preferably has facilities for
rotation and distribution of the layer of adhesive over the
non-active surface (generally the rear surface), as well of the
thus formed reconstituted wafer so as to obtain even distribution
of the epoxy.
[0057] The thus formed reconstituted wafer 686 is thinned at its
non-active surface as by a grinding apparatus 684 using an abrasive
687. The wafer is then etched at its non-active surface, preferably
by photolithography, such as by using conventional spin-coated
photoresist, using a mask exposure machine 692 for the exposure of
light sensitive photoresist 690 through the mask 691 and later
etching the silicon in a bath 693 using solution 699. The etched
wafer is bonded on the non-active side to an adhesive or protective
layer 1000, which can be epoxy or other adhesive by bonding
apparatus 694, which may be essentially the same as apparatus 685,
to produce a doubly bonded wafer sandwich. The wafer may then by
bonded to a second or more wafers.
[0058] Notching apparatus 695 partially cuts the stacked assembly
in a method of forming a stacked package as described above with
reference to FIGS. 2-9. The notched stacked assembly then is
subjected to anti-corrosion treatment in a bath 696, containing a
chromating solution 698. Alternatively, a chemical etching
apparatus (not shown) may be used to form notches exposing one or
more traces or openings exposing the traces of respective
microelectronic elements.
[0059] Conductive layer deposition apparatus 700 (FIG. 19), which
operates by vacuum deposition techniques, is employed to produce a
conductive layer on one or more surfaces of each die of the wafers.
Configuration of the contact strips or lead bridges is carried out
preferably by using conventional electro-deposited photoresist 701.
The photoresist 701 is applied to the stacked assembly 707 of
reconstituted wafers in a photoresist bath assembly 702. The
photoresist 701 is preferably light configured by a UV exposure
system 704, which may be identical to system 692, using a mask 705
to define suitable etching patterns. The photoresist is then
developed in a development bath 706, and then the wafer is etched
in a metal solution 708 located in an etching bath 710, thus
providing a conductor configuration.
[0060] The exposed conductive strips are then plated, preferably by
electroless plating apparatus 712. The stacked wafers are then
diced into individual prepackaged integrated devices as described
above with reference to FIGS. 9 and 10. Preferably, the dicing
blade 714 should be a diamond resinoid blade having a thickness of
about 4 to about 12 mils, such thickness preferably corresponding
to the width of the saw lanes 23, 25 (FIG. 1A).
[0061] While the techniques and implementations have been described
with reference to exemplary embodiments, it will be understood by
those skilled in the art that various changes may be made and
equivalents may be substituted for elements thereof without
departing from the scope of the appended claims. In addition, many
modifications may be made to adapt a particular situation or
material to the teachings without departing from the essential
scope thereof. Therefore, the particular embodiments,
implementations and techniques disclosed herein, some of which
indicate the best mode contemplated for carrying out these
embodiments, implementations and techniques, are not intended to
limit the scope of the appended claims.
* * * * *